A communication system can be seen as a facility that enables communications between two or more entities such as a communication device, e.g. mobile stations (MS) or user equipment (UE), and/or other network elements or nodes, e.g. Node B or base transceiver station (BTS), associated with the communication system. A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how that should be achieved.
Wireless communication systems include various cellular or otherwise mobile communication systems using radio frequencies for sending voice or data between stations, for example between a communication device and a transceiver network element. Examples of wireless communication systems may comprise public land mobile network (PLMN), such as global system for mobile communication (GSM), the general packet radio service (GPRS) and the universal mobile telecommunications system (UMTS).
A mobile communication network may logically be divided into a radio access network (RAN) and a core network (CN). The core network entities typically include various control entities and gateways for enabling communication via a number of radio access networks and also for interfacing a single communication system with one or more communication systems, such as with other wireless systems, such as a wireless Internet Protocol (IP) network, and/or fixed line communication systems, such as a public switched telephone network (PSTN). Examples of radio access networks may comprise the UMTS terrestrial radio access network (UTRAN) and the GSM/EDGE radio access network (GERAN).
A geographical area covered by a radio access network is divided into cells defining a radio coverage provided by a transceiver network element, such as a Node B. A single transceiver network element may serve a number of cells. A plurality of transceiver network elements is typically connected to a controller network element, such as a radio network controller (RNC). The logical interface between an RNC and a Node B, as defined by the third generation partnership project (3GPP), is called as an Iub interface.
Physical channels are transmission channels, such as radio channels, provided between transmitters and receivers. A transport channel defines characteristics, such as coding, interleaving and mapping onto physical channels, with which data is transported over the air interface. A logical channel is an information stream for a particular type of information carried by a transport channel. Wideband code division multiple access (WCDMA) is an example of a channel multiplexing technique for mapping transport channels onto physical channels in a 3GPP network.
In different communication systems, different transfer modes may be used. Examples of transfer modes may comprise circuit mode, packet mode, frame mode and cell mode. The circuit mode is used, for example, in the PSTN and the GSM. The packet mode is used, for example, in the IP networks and in the GPRS. The frame mode may be used, for example, to interconnect local are networks (LANs). The cell mode comprises, for example, Asynchronous Transfer Mode (ATM).
Asynchronous Transfer Mode (ATM) is a cell-based technique for multiplexing and transfer of information used, for example, in the UTRAN. In the ATM, an information flow with different and varying bit rates, comprising different services, such as voice, data and video, is organised into one common cell flow. ATM uses fixed-length cells of 53 bytes having a cell header of five octets and a user part, also called payload, of 48 octets. ATM creates fixed logical channels between two points when data transfer begins. The logical channels are identified by an address in the cell header. The address is divided into two levels, virtual channels (VC) and virtual paths (VP). The header thus includes a virtual channel identifier (VCI) and a virtual path identifier (VPI) identifying a connection in the ATM network. A virtual path is a path between two network nodes and a virtual channel is a route for a specific connection on the virtual path. The physical transmission medium, such as an optical fibre, carries several virtual paths.
In the ATM, a protocol reference model defines layers of the ATM. The lowest layer is a physical layer transporting the ATM cells created in a layer above, in an ATM layer. Above the ATM layer, an ATM adaptation layer (AAL) maps bit streams from higher layers onto the ATM layer. The AAL comprises different protocols, namely AAL0, AAL1, AAL2, AAL3/4 and AAL5, for example, for supporting different service classes. The purpose of the AAL2, i.e. the ATM adaptation layer type 2, is to realise connections of variable bit rate on a common AAL2 virtual path. The AAL2 establishes an ATM virtual channel connection (VCC).
In the 3GPP WCDMA UTRAN, ATM switching may be used. For example, downlink Common Transport Channels, such as a Forward Access Channel (FACH) and a Paging Channel (PCH), each typically have a separate transport bearer, that is, a dedicated AAL2 connection over the Iub interface. In other words, for example relating to the FACH, one Iub FACH data stream is carried on one transport bearer and for each FACH in a cell, a transport bearer must be established over the Iub interface, as defined in the 3GPP TS 25.430 V3.6.0 (2001-06), Third Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub Interface: General Aspect and Principles (Release 1999), paragraph 4.5.1.
For a reliable transport for each common transport channel over the Iub interface, an AAL2 connection for each common transport channel is usually reserved based on the maximum bit rate of the channel. However, the common transport channels can use a single control channel, such as a Secondary Common Control Physical Channel (SCCPCH), over the air interface depending on the physical channel configuration used. Thus, the common channels cannot all send using the maximum bit rate configured for each channel in a single time interval (TTI). Scheduling, or admission control, of the SCCPCH may be managed by a medium access control-common/shared channel (MAC-C/SH) entity in an RNC, ensuring that the amount of traffic send by the RNC to a transceiver network element does not exceed the capacity of the control channel the common channels in question are using. If an AAL2 connection is reserved for all the common channels based on the configured maximum bit rate, some of the transport capacity may be unnecessarily reserved. This may lead to inefficient usage of available transport resources over the Iub interface.
Similar situation may arise, for example, when a Downlink Shared Channel (DSCH) concept is used. Each transport bearer is provided by a separate AAL2 connection over the Iub interface. A MAC-C/SH handles the scheduling and ensures that the capacity of a Physical Downlink Shared Channel (PDSCH) is not exceeded. However, each of the user data streams carried over the separate AAL2 connections can use momentarily the whole capacity of the PDSCH. Thus, the AAL2 connections over the Iub interface need to be reserved based on the maximum bit rate of an individual user data stream. This again may lead to inefficient usage of transport resources over the Iub.
For other channels, similar conditions may apply. In accordance with 3GPP TS 25.434 V6.1.0 (2004-03), Third Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub Interface Data Transport and Transport Signalling for Common Transport Channel Data Streams (Release 6), paragraph 5.2, ATM and AAL2 may be used at the standard transport layer for Iub Random Access Channel (RACH), Common Packet Channel (CPCH), FACH, PCH, DSCH, High Speed Downlink Shared Channel (HS-DSCH) and Uplink Shared Channel (USCH) data streams.
It shall be appreciated that these issues are not limited to any particular communication environment, but similar issues may occur in other communication systems as well.
Patent Application US 2002/0181470 A1 proposes a solution for bandwidth efficient quality of service separation of AAL2 traffic. In the US 2002/0181470 A1, bandwidth of an individual AAL2 path comprising an AAL2 path group is contributed to a total bandwidth of the AAL2 path group rather than to the individual AAL2 path exclusively. An admission decision regarding a connection seeking to use an AAL2 path belonging to the AAL2 path group is based on available bandwidth of the AAL2 path group rather than available bandwidth of an individual AAL2 path. ATM VCCs, which comprise the AAL2 path group, are transported on a virtual path together with ATM VCCs of a different type.
It might be desired to be able to reserve AAL2 capacity in the Iub based on a real usage of AAL2 resources in the Iub. This might help to avoid unnecessary reservations of transport resources. This might increase efficiency of a use of transport resources in the Iub interface.